近日，美国明尼苏达大学Peter J. Makovicky团队报道了阿根廷化石改写了令人困惑的恐龙进化史。2026年2月25日，该项成果发表在《自然》杂志上。

阿尔瓦雷斯龙类是一种主要为小型体型的神秘兽脚类恐龙类群，主要见于亚洲和南美洲的侏罗纪至白垩纪时期。晚白垩世的阿尔瓦雷斯龙类演化出适应挖掘的特化前肢、增生的微小牙齿及敏锐的感觉能力，被解读为食蚁性动物。学界曾假设该类群在食性特化过程中伴随有体型微型化演化。根据传统观点，南美洲的零散化石类群相对于晚白垩世亚洲亚科小驰龙类构成并系类群，这种不连续的生物地理分布被归因于扩散事件。

研究组描述了塞罗波利西亚阿尔纳谢蒂龙的骨骼化石——就他们所知，这是迄今最完整且体型最小的南美洲分类单元。同时研究组在北半球历史分类群中识别出两个阿尔瓦雷斯龙类物种。系统发育分析将阿尔纳谢蒂龙置于非阿尔瓦雷斯龙类的基干位置，表明南美洲分类群呈现复系性。结合新识别的分类单元，该生物地理学分析推断阿尔瓦雷斯龙类起源于泛大陆的祖先分布，地理隔离主导了该演化支的早期历史。阿尔纳谢蒂龙在体型较大的近缘类群中处于基干分支位置，这一发现修正了阿尔瓦雷斯龙类体型演化的最佳拟合模型——研究结果不支持微型化演化假说，反而揭示该类群在狭窄体型范围内存在重复演化模式。

附：英文原文

Title: Argentine fossil rewrites evolutionary history of a baffling dinosaur clade

Author: Makovicky, Peter J., Mitchell, Jonathan S., Meso, Jorge G., Gianechini, Federico A., Cerda, Ignacio, Apestegua, Sebastian

Issue&Volume: 2026-02-25

Abstract: Alvarezsauroids are an enigmatic clade of predominantly small-bodied theropod dinosaurs that are known mainly from the Jurassic to Cretaceous periods of Asia and South America1,2,3. Late Cretaceous alvarezsauroids possess specialized forelimbs adapted for digging4,5, minute supernumerary teeth and heightened sensory capacities6, and are interpreted as myrmecophagous. They are hypothesized to exhibit evolutionary miniaturization coupled to their dietary specialization2. Fragmentary South American taxa are traditionally arrayed as a paraphyletic grade with respect to the Late Cretaceous Asian subclade Parvicursorinae2,3, invoking dispersal to explain their disjunct distributions. Here we describe a skeleton of the alvarezsauroid Alnashetri cerropoliciensis7 representing to our knowledge the most complete and smallest South American taxon to date. We also recognize two alvarezsauroids among historic taxa from the Northern Hemisphere. Phylogenetic analysis recovers Alnashetri among basal non-alvarezsaurids, rendering South American taxa polyphyletic. Combined with the new taxa recognized here, our biogeographical analyses infer a Pangaean ancestral distribution for Alvarezsauroidea, with vicariance dominating the early history of the clade. The early branching position of Alnashetri among larger-bodied relatives revises best-fit models of body size evolution in alvarezsauroids—we find no support for evolutionary miniaturization but, rather, find support for repeated evolution within a narrow body size range.

DOI: 10.1038/s41586-026-10194-3

Source: https://www.nature.com/articles/s41586-026-10194-3